You could do the internal BASIC upgrade.
Read this: http://www.atarimax.com/myide_old/docum ... 200xl.html
You can pop the BASIC-eprom in the TOP socket and the OS in the bottom.
Need to change the MMU.....
MyBIOS in ROM would be the best option.
Update your MyIDE to the latest MyBIOS? (What MyBIOS does your boot-screen show?)